It is thermally conductive, as you can see in the above photo. The black needle is over the i in the diamond name on the display.

The refractive index is 1.718-1.732. Birefrengence is 0.014. A uniaxial interference figure is visible in the polariscope. A weak orange colour is visible under the SWUV lamp. No absorption bands are visible with the hand spectroscope.

One colourless bromellite crystal was found near Gilimala, Sri Lanka in March 1999. It was cut into 17 faceted stones the largest weighing 2.80 ct. the next biggest was 1.90 ct, the next was 0.68 ct. The remaining 14 cut stones were all below 0.50ct in.weight.

The pictured 0.19 ct. faceted stone was from the same crystal and was a gift to me from Mr. Palitha Gunasekera of Ratnapura, Sri Lanka. It was Mr. Gunasekara who purchased this stone, and recognizing it's uniqueness, sent it to the Gemological Institute of America for advanced testing.

The 0.41 ct stone, pictured above, I purchased from Mr. Gunasekara in March 2004. It was the last stone of the original lot remaining in Sri Lanka.

It is believed this is the only Sri Lankan crystal found so far. Since that time many people have been looking but no one has found another bromellite in Sri Lanka. I don't expect to ever obtain another.

Bromellite in very small sizes (to small to cut) has been found in Sweden as well as in the Ural mountain area of Russia.

Gems & Gemology has described the three largest stones cut from this crystal with a colour photo as well as four bromellite internal inclusion photos (natural and synthetic) in the Fall 2002 issue, V.38 N.3 pages 250-251.

Bromellite is chemically BeO. It's hardness is 9. Specific gravity is 3.01-3.03. The crystal system is hexagonal. Because of the high beryllium content (about 36%) the dust and fumes can be toxic, when it is being cut or formed.

The inclusion photo above taken of a 0.41 ct bromellite (70x), shows some 2 phase inclusions as well as some colourless pointed inclusions . Other colourless inclusions seem to display crystal faces.
I have sold both of these gemstones, the 0.41 ct stone to a collector from The Netherlands and the 0.19 ct bromellite to a collector from California USA. The largest gemstone the 2.81 ct was purchased from Mr Gunasekara for a large Swiss based Sri Lanka gemstone collection.

Synthetic bromellite (see photo below)
According to D. Elwell (1979) synthetic bromellite was made by the flux method in the 1960's by Rockwell International of California.The proposed use was as heat sinks for semiconductors in electronics. Richard Liddicoat (1964) was the first to describe the gemological properties of synthetic bromellite.
K. Nassau (1978) mentions that synthetic bromellite has a thermal conductivity higher than gold and close to copper and could be confused with diamond when using a thermal reaction tester.
O'Donoghue(1976) mention a further 8 scientific papers on synthetic bromellite. Robert Webster (1970) as well as N.R. McDonald (1967) also describe it.

References
Elwell D., Man-Made Gemstones 1979 John Wiley & Sons pg. 121
Liddicoat R.T., Unusual refractometer reading (synthetic bromellite) G&G 1964, XI N5, p. 150
McClure S.F. and Muhlmeister S., Bromellite, Gem Trade Lab Notes, Gems & Gemology Vol. 38 no. 3, Fall 2002 pages 250-251
McDonald N.R., Synthetic Beryllia crystals, Australian Gemmologist 1967, 75, 7-9
Nassau K., A Test of the Ceres Diamond Probe Gems & Gemology Winter 1978-1979 V. XVI N. 4 Pg. 98-103
O"Donoghue Michael, Synthetic Gem Materials, 1976, Worshipful Company of Goldsmiths, London pg. 38-39
Webster Robert, Modern Synthetic Gemstones, J. of Gemm. V. 12 N. 4 Oct. 1970 pg 101-148